The proinflammatory cytokine interleukin-1 (IL-1) functions in the generation of systemic and local responses to infection, injury and immunological challenges. The importance of IL-1 in inflammation has been demonstrated by the ability of the highly specific IL-1 receptor antagonist protein (IL-1Ra, or IRAP) to relieve inflammatory conditions (for review, see, e.g., Dinarello, Cytokine Growth Factor Rev. 8:253–265 (1997)). IL-1 is produced primarily by activated macrophages and monocytes, and is involved in lymphocyte activation, fever, leukocyte trafficking, the acute phase response, cartilage remodeling and other processes. IL-1 exerts its effects by binding to a receptor, IL-1RI, located on the plasma membrane of responsive cells. Among the results of IL-1 binding to the IL-1RI receptor is the activation of the NF-κB transcription factor, ultimately leading to the expression of numerous genes involved in inflammation, such as cytokines, growth factors, immunoreceptors, and cell adhesion molecules (for review, see, e.g., Lee, et al., J. Clin. Pharmacol. 38(11):981–93 (1998)).
Several proteins have been discovered to mediate signal transduction following IL-1RI activation, ultimately leading to the activation of NF-kB. For example, the IL-1R accessory protein, IL-1RAcP, has been shown to associate with the IL-1RI receptor following binding to IL-1, thereby initiating the signal transduction cascade (Greenfeder, et al., J. Biol. Chem. 270(23):13757–65 (1995)). In addition, three IL-1 receptor-associated kinases (IRAKs) have been identified, IRAK (“IRAK-1;” Cao, et al., Science 271:1128–1131 (1996)), IRAK-2 (Muzio, et al., Science 278:1612–1615 (1997)), and the monomyeloic cell-specific IRAK-M (Wesche, et al., J. Biol. Chem. 274:19403–10 (1999)). IRAK has been shown to be phosphorylated and to associate with IL-1RI in an IL-1 dependent manner. In addition, the MyD88 protein has been shown to mediate the association of IRAK proteins to the activated IL-1 receptor (Wesche, et al., 7:837–47 (1997)). Also, TRAF6 transduces the IRAK signal to downstream effector molecules (Cao, et al., Nature 383:443–6 (1996)). The IRAK proteins, as well as MyD88, have been shown to play a role in transducing signals other than those originating from IL-1R receptors, including signals triggered by activation of IL-18 receptors (Kanakaraj, et al. J. Exp. Med. 189(7):1129–38 (1999)) and LPS receptors (Yang, et al., J. Immunol. 163:639–643 (1999); Wesche, et al., J. Biol. Chem. 274:19403–10 (1999)). Overexpression of IRAK-2 and IRAK-M has been shown to be capable of reconstituting the response to IL-1 and LPS in an IRAK deficient cell line.
The IL-1 signal transduction cascade is analogous to a signaling cascade in Drosophila melanogaster that is involved in the establishment of dorsal ventral polarity during the early development of Drosophila embryos. Specifically, in Drosophila, the extracellular ligand Spaetzle binds to a receptor called Toll, which shares homology to IL-1R. In addition, a serine/threonine kinase acting downstream of Toll activation, Pelle is homologous to IRAK kinases (Cao, et al., Science 271:1128–1131 (1996); Muzio, et al., Science 278:1612–1615 (1997); Wesche, et al., J. Biol. Chem. 274:403–410 (1999)). Finally, activation of the Toll receptor results in the activation of the transcription factor Dorsal, which is homologous to NF-κB. Dorsal is inhibited in Drosophila cells by Cactus, which is itself homologous to the NF-κB inhibitor IκB.
The present invention is based on the identification of a novel member of the IRAK family, IRAK-4. Nucleic acid and protein sequences for IRAK-4 are provided, as are methods of making IRAK-4 nucleic acids and proteins. Also provided are methods of using IRAK-4 polynucleotides and polypeptides, including methods of using the herein-disclosed sequences to isolate compounds useful in the treatment or prevention of any of a number of inflammatory diseases and conditions.